What is an Amphibian? - Definition & Characteristics

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  • 0:00 Definition of an Amphibian
  • 1:00 Characteristics of Amphibians
  • 3:23 Orders of Amphibians
  • 5:05 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

An amphibian is a class of animals that live their lives both in and out of water. There are three orders within this class, the most common of which includes frogs and toads. Learn more about these animals, and take a short quiz at the end.

Definition of an Amphibian

You may remember catching frogs in the summertime as a child. It was no easy feat, sneaking up on the slippery buggers and trapping one in your hands. Perhaps near a pond, the frogs could make a quick escape into the water with a splash. Frogs are probably the most recognizable and certainly the most abundant members of a class of animals known as amphibians. But, frogs and toads are certainly not the only members of this group.

Amphibians are animals that belong to the phylum Chordata. Among other things, animals in the Chordata phylum have a backbone. Amphibia is a class within the Chordata phylum, and there are three subgroups, or orders, included. Our well-known friends the frogs and toads belong to the order Anura. However, two additional orders, Urodela and Apoda, also belong here. We will take a closer look at all of these animals as we explore the world of amphibians.

Characteristics of Amphibians

The word amphibian means dual lives. You may have seen an amphibious car, one that drives on land and then heads straight into the water and functions like a boat. In the world of amphibians, this idea of dual lives pertains to the youngster stage and quite different adult stage that most of them undergo. Let's take a closer look at frogs as an example.

Frog babies hatch into water as tiny tadpoles with no legs or lungs. Closely resembling fish, these frog youngsters swim using their tails and breathe through gills. And then a dramatic metamorphosis occurs. Losing the tail and the gills, the tadpole grows legs and transforms into a frog. Our adult frog crawls up onto the shore, now spending time both in and out of the water. Hence, a dual life.

Amphibians have other defining trademarks that make them who they are. First, they are cold-blooded creatures. If you enjoy warm and fuzzy pets, an amphibian may not be the one for you. Amphibians are at the mercy of the environment around them. They have to regulate their temperature by physically moving to or away from the heat source. If it's an extremely hot day, you'll probably find them lounging in the pond.

Another important characteristic of this class of animals is the fact that amphibians have moist, scaleless skin. Think back to catching those frogs. You could feel the thin, slippery layer covering its body. It is for this reason that frogs and their relatives must stay close to water at all times. And, it's not just because they enjoy swimming.

Amphibians absorb their water right through their skin. Unlike their reptile cousins that have thick scales covering their bodies, the skin of an amphibian is extremely thin and fragile. This allows water to penetrate but also puts them at high risk of dehydration. And so, their favorite hangouts are watery destinations such as ponds, lakes, and swamps.

An amphibian's skin has another crucial job, which is gas exchange. Frogs and their relatives actually breathe through their skin as adults. Although adult amphibians do have lungs, they function rather poorly. Oxygen gas is absorbed, and carbon dioxide is released, right through the very thin covering of these creatures. Thus, it is even more important for them to keep their skin moist and protected.

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